Developer Reference

  • 2020.2
  • 07/15/2020
  • Public Content
Contents

?lacn2

Estimates the 1-norm of a square matrix, using reverse communication for evaluating matrix-vector products.

Syntax

call slacn2
(
n
,
v
,
x
,
isgn
,
est
,
kase
,
isave
)
call dlacn2
(
n
,
v
,
x
,
isgn
,
est
,
kase
,
isave
)
call clacn2
(
n
,
v
,
x
,
est
,
kase
,
isave
)
call zlacn2
(
n
,
v
,
x
,
est
,
kase
,
isave
)
Include Files
  • mkl.fi
Description
The routine estimates the 1-norm of a square, real or complex matrix
A
. Reverse communication is used for evaluating matrix-vector products.
Input Parameters
n
INTEGER
.
The order of the matrix
A
(
n
1
).
v
,
x
REAL
for
slacn2
DOUBLE PRECISION
for
dlacn2
COMPLEX
for
clacn2
DOUBLE COMPLEX
for
zlacn2
.
Arrays, size (
n
) each.
v
is a workspace array.
x
is used as input after an intermediate return.
isgn
INTEGER
.
Workspace array, size (
n
), used with real flavors only.
est
REAL
for
slacn2
/
clacn2
DOUBLE PRECISION
for
dlacn2
/
zlacn2
On entry with
kase
set to 1 or 2, and
isave
(1) = 1
,
est
must be unchanged from the previous call to the routine.
kase
INTEGER
.
On the initial call to the routine,
kase
must be set to 0.
isave
INTEGER
.
Array, size (
3
).
Contains variables from the previous call to the routine.
Output Parameters
est
An estimate (a lower bound) for norm(
A
).
kase
On an intermediate return,
kase
is set to 1 or 2, indicating whether
x
is overwritten by
A
*
x
or
A
T
*
x
for real flavors and
A
*
x
or
A
H
*
x
for complex flavors.
On the final return,
kase
is set to 0.
v
On the final return,
v
=
A
*
w
, where
est
= norm(
v
)/norm(
w
)
(
w
is not returned).
x
On an intermediate return,
x
is overwritten by
A
*
x
, if
kase
= 1
,
A
T
*
x
, if
kase
= 2
(for real flavors),
A
H
*
x
, if
kase
= 2
(for complex flavors),
and the routine must be re-called with all the other parameters unchanged.
isave
This parameter is used to save variables between calls to the routine.